Screw jack



A. L. JOHNSON SCREW JACK Filed March 24. 1925 J M/ J J i f 4, d VAVWIWA,

x x Y Y Y N June 9, 1925.

Patented June 9, 1925.

UNITED STATES ALVIN L. JOHNSON, 0F SPRINGFIELD, MASSACHUSETTS.

` SCREW JACK.

Application filed March 24, 1925.

To aZZ whom t 'may concern:

Be it known that I, ALviN L. JOHNSON, a citizen of the United States,residing at Springfield, in the county of Hampden and State ofMassachusetts, have invented a new and useful Screw Jack, of which thefollowing is a specification.

This invention relates to a screw jack of the type in which the meansfor lifting the load has a double travel. That is, it moves upwardly onan element which supports it which itself also moves upwardly at thesame time so that the load support will rise to a height of more thantwice the height of the ack when collapsed. Although this jack iscapable of general use it is particularly adapted for automobile use onaccount of the difficulties that have been encountered due to the use ofballoon and other over-size tires.

The principal objects of this invention are to provide a jack of thiskind in which the work supporting member that projects up out of thejack casing is entirely without screw threads that are exposed, thusavoiding the injuring of the screw threads in the use and abuse of thejack and always keeping them protected from dirt, dust and metalparticles.

Another object of the jack is to improve the means for guiding the worksupporting element so that it will be guided always at a point nearerits upper end than has been the case heretofore and will also lhave aguide at its lower end;

Another object of the invention is to provide a more simple constructionthan has been provided heretofore in this type of jack.

Reference is to be had to the accompanying drawings, in which Fig. 1 isa central sectional view of a jack constructed in accordance with thisinvention, shown in its lowermost position; and

Fig. 2 is a plan of the jack.

The jack preferably is made with -a standard or casing 10 having acomparatively wide base. The main part of this lstandard is in the formof a vertical cylinder having an internal screw thread. In this screwthread turns a screw 11 which is internally and externally threaded inopposite directions all the way from top to. bottom. To the top of thisscrew is fixed a gear 12 or other element for rotating it so as to causeit to rise in the internal screw thread in Serial No. 18,031.

the casing 10. The gear is shown as operated by a pinion 13 and shaft 14for the attachment of a handle.

In the interior of the internally vthreaded screw 1l T provide a screw22 meshing with the internal screw threads of the screw and thereforecapable of being moved'up and dougn therein by the turning of the screw.In the top of this nut is a square or other non-circular hole forreceiving a similar shaped projection 15 on a plunger 16. This plungeris of square or other non-circular shape and obviously it is'iiXed tomove with the screw 22.

0n top of the casing 10 I provide an outer casing 17 in which the gears12 and 13 are housed and which has a bearing for the shaft 14. Thiscasing surrounds the upper gear 12 and is provided with a flat top 18bearing against the top of the gear to receive the thrust. The top hasin the center thereof a perforation 19 of the same shape as the plunger16. The plunger is of the same size all the way from the top to thebottom and the opening 19 is broached or otherwise finished so as to fitthis plunger and constitute an accurate guide for it.

In the operation of the jack. assuming it to be in the collapsedposition shown in Fig. 1, the shaft and gears are turned by means of thehandle. This results, in the first place, in turning the screw 11 whichmoves it up on account of its engagement with the stationary internalscrew threads of the casing 10. This screw therefore rises, taking withit the casing 17 and all the parts supported thereby. But simultaneouslyanother action takes place, namely the rising of the plunger 16 in thescrew due to the fact that the nut does not turn. This plunger risesrelatively to the screw just as fast as the screw rises. Therefore I gettwice the velocity of travel of the plunger that I do of the screw.-Also, the plunger rises so that its upper surface eventually gets to aheight approximately three times the elevation of the jack whencollapsed, as shown in Fig. 1.

Furthermore, it will be seen that on account of the guide furnished bythe hole 19 and the stabilization of the plunger by the screw 22 whichis at a considerable disjacks on the market because this guide 19 islocated at a considerably higher point than usual. When the plungerrises to the top in the former types of jack there was only one guidingor stabilizing element below the gear. so there was a chance to sway,especially after long wear. In this case we have the nut below and inaddition the guide 19 which is above the gear. Thus, the two guiding andstabilizing points are at a maximum distance apart in this type of ackand the upper one is higher than in any such jack on the market. Thecasing 17 is prevented from turning by one or more studs 20 and slots21.

As stated above. a very important advantage of this jack lies in thefact that all the screw threads are enclosed in the casing and protectedfrom dust and dirt and particularly metal particles. This is anadvantage in the ordinary use of a jack in the Shop and of still moreadvantage where it is handled out ou the road and may be tipped over andthe screw threads filled with dirt, stones, cement and whatever else maybe in the roadway. There is a high degree of protection against theentrance of dirt into the casing because of the guiding lit of theopening 19. This is the only opening that is exposed.

This is a comparatively inexpensive jack to make and put on the marketand it contains no springl latches that are likely to be placed wherethey cannot be repaired. On account of their absence the cost ofmanufacture and assembly is very small indeed.

Although I bave illustrated and described only a single form of theinvention I am aware of the fact that modifications can be made thereinby any person skilled in the art without departing' from the scope ofthe invention as expressed in the claims.

Therefore I do not wish to be limited to all the details ot constructionherein shown and described, but what I do claim is 1. In a screw jack,the combination of a casing having an internal screw thread with ahollowscrew fitting in said thread and having itself an internal screwthread, a screw within the last named screw thread fitting the same, aSquare plunger extending upwardly from the second screw, means at thetop of the casing'for turning the hollow screw, and a second casingsurrounding the turning means and having a guide having a square openingfor preventing the plunger from turning, whereby when the hollow screwis turned it will rise and the plunger and second screw will rise withinit ata higher speed.

2. In a screw jack, the combination of a cylindrical casing having aninternal screw thread, a hollow screw movable up and down in said screwthread and provided with an internal screw thread, a screw fitting inthe second internal screw thread and movable from the top to the bottomthereof, a non-circular plunger extending upwardly from the last namedscrew to the top of the first screw, a gear fixed to the top of thehollow screw for turning it, and a second casing surrounding the gearand having a passage therethrough fitting the plunger, whereby theplunger will be prevented from turning.

3. In a screw jack, the combination of a easing having an internal screwthread, a hollow screw movable up and down in said screw thread andprovided with an internal screw thread, all the way to the bottom, anon-circular unthreaded plunger as long as the screwv and locatedtherein. a short screw on the bottom of the plunger fitting the internalthread, a gear fixed to the top of the screw for turning it, and a guidelocated above the gear and fitting the noncircular plunger, whereby theplunger is guided and stabilized at two points always at considerabledistance apart.

In testimony whereof I have hereunto afl'ixed my signature.

ALVIN L. JOHNSON.

CTI

